This invention relates to a hydraulic brake system for automotive vehicles with a master brake cylinder connected to an unpressurized reservoir and with a brake line connected to a working chamber of the master brake cylinder and leading to pressure control valves of a brake slip control device. The pressure control valves are followed by at least on wheel brake, with the working chamber or the master brake cylinder being connectable to a pressure medium source upon the start of the brake slip control device.
In brake systems of this type, for repeated actuation of the wheel brake after a relief in pressure, a pressure medium amount is required during the operation of the brake slip control device, which far exceeds the delivery capacity of the master brake cylinder. Thus, during the operation of the brake slip control device, it is necessary to supply the wheel brake, independently of the master brake cylinder, with pressure medium from an additional pressure medium source such as an energy supply system.
A brake system is known from German published patent application No. P 34 39 258 where a hydraulic-energy-supply-system-fed brake booster is provided for the actuation of the master brake cylinder. In this brake system, the brake line is connectable with the booster chamber of the brake booster by way of an electromagnetically operable control valve of the brake slip control device and by way of a non-return valve following the valve. This is for the purpose of supplying the wheel brake cylinders with pressure medium from the energy supply system during the operation of the brake slip control device. Further, a controllable non-return valve is provided between the master brake cylinder and the connection point of the control valve which can be switched into a locking position by means of the pressure supplied by way of the control valve. In the locking position the pressure medium is only able to flow back to the master brake cylinder. Thereby, the master brake cylinder is kept in a ready position during the operation of the brake slip control device. This solution is limited, however, to brake systems with a hydraulic brake booster. Such brake systems, however, are relatively intricate and expensive and thus are generally not considered for use in smaller vehicles. A further disadvantage of this prior brake system is that the readiness of the hydraulic brake booster and brake slip control device are interdependent.
Depending on the vehicle type, brake calipers with varying sizes for clearance are built into the disc brakes. So as to be able to use one brake system for different clearances, the length of the master brake cylinder must be rated such as to conform with the largest needed clearance. Thus, in case of a larger clearance, there will result a relatively long pedal travel. However, master brake cylinders with great overall lengths are not desirable.
Thus, stepped master brake cylinders with differently effective diameters, coordinated with the respective clearance, are being used so as to avoid long pedal travels and excessive overall lengths. Such stepped master brake cylinders, however, are relatively intricate and expensive.
It is thus an object of the present invention to further develop a brake system of the type mentioned above so as to ensure that the same master brake cylinder can be used in brake systems of different vehicle types the wheel brakes of which have clearances differing in size, without the master brake cylinder having a long pedal travel and thus a great overall length.